Wednesday, 25 May 2011

Great balls of......water

I showed you how the surface tension of water in space allows for water balls.  These balls can also be achieved due to the strong surface tension of water on specialized surfaces.  On a superhydrophobic surface the same thing happens and balls of water are in fact made.  These balls of water can be electrostatically charged and manipulated.  Hydrophobic meaning 'water hating' are surfaces that cause water not to spread out all over the table like your spilled beer.  Rather it allows the solid surface to be repel the wettability of the water.  The water then looks like a ball in this picture below:

with a contact angle (between the solid surface, air and water) is trying to go to around 180 degrees.  A natural superhydrophobic surface is that of a lotus plant.  Its waxy leaves repel water giving what they term The Lotus Effect.  This Lotus Effect self cleans the lotus plant allowing dirt to be removed and increasing the accessibility for photosynthesis.

With the adhesion of silica nanoparticles, contact angles as high as 162° are achieved. Using silica nano-particles is also of interest to develop transparent hydrophobic materials for car windshields and self-cleaning windows, jeans that do not get dirty or microfluidic devices like some dudes at Aalto possibly want to build after making this article.

Reposted from here:

Water drops move on water-repellent trackss like marbles in our childhood toys


Researchers at Aalto University have developed a simple and efficient method for moving liquid drops in an almost totally water-repellent track. Drops move in open tracks, machined in metal or Si wafers, using gravity or using electrostatic charge. There is also a possibility to split drops in two with a blade mechanism developed for the track. For the droplet transport method now developed, there are excellent application possibilities, for example, in biochemical and medical analysis devices. The research findings have been recently published in Advanced Materials, a respected scientific journal.

Digital microfluidics, a relatively new field in microfluidics, studies controlling and analyzing single liquid droplets instead a continuous flow of liquids in channels. The research requires a multidisciplinary approach, and thus, it has been performed in cooperation and interaction between physicists and chemists from Aalto University, University of Helsinki and Technion (Israel).

“Future analysis devices may employ the presented method because of the low cost and efficiency of the droplet transport.”, tells undergraduate student Henrikki Mertaniemi, who performed the research under supervision of Dr. Robin Ras (Molecular Materials group, Dept. Applied Physics) in the context of his special assignment.

Link to the publication:

Links to the videos showing water drops passing multiple curves in a superhydrophobic track with a width of 1.5 mm. The plate is tilted only slightly.

Superhydrophobic knife

Electrostatic actuation of a water droplet in a superhydrophobic track:

Superhydrophobic Track (soon kids will be playing with this everywhere)